Plug Housing
D38999/26FA35AN
Mil-Spec Circular Connector Reference
MIL-DTL-38999 Connectors
MIL-DTL-38999 is the high-density, severe-environment circular connector family for aircraft, defense, marine, and rugged equipment harnesses. A build still has to choose the exact series, shell, insert, contacts, finish, backshell, and tooling.
MIL-DTL-38999CAD / Connector Bay
I / II / III / IVSeries
9-25Shell Sizes
Removable CrimpContacts
SeriesI / II / III / IV
Shell Sizes9-25
ContactsRemovable Crimp
EnvironmentSealed / Hermetic
What MIL-DTL-38999 Covers
MIL-DTL-38999 is not one connector. It is a family of high-density circular connectors for aircraft, defense, marine, test, and rugged equipment wiring. The spec covers multiple coupling styles with sealed, removable-contact environmental connectors and hermetic variants.
The value is packaging and discipline: many circuits in a compact round shell, positive polarization, serviceable contacts, environmental sealing, and backshell hardware for strain relief and shield termination.
The main quote inputs are series, shell size, shell style, insert arrangement, contact gender, keying, finish class, backshell exit and strain relief, contacts and tooling, and any QPL constraints.
MiniProto RoleBuilt Assembly
OEM pages from Amphenol, Glenair, and similar manufacturers sell connector parts. MiniProto turns the selected plug, receptacle, contacts, backshells, wire, labels, and test requirements into a built harness assembly with prototype-friendly ordering.
Representative Catalog Parts
Source-backed parts that illustrate the family. Final selection still depends on series, shell, insert, keying, finish, backshell, and QPL requirements.
Socket Contact
M39029/56-348
Protective Cover
D38999/33F9N
When The Connector Earns Its Keep
Good fit
- Aircraft, defense, marine, robotics, and rugged equipment harnesses.
- Bulkhead pass-throughs, sealed disconnects, shielded cable breakouts, and blind-mate interfaces.
- Programs that need controlled part numbers, finish classes, traceability, or QPL sourcing.
Usually avoid
- Low-cost indoor equipment where sealed circular hardware adds no value.
- Early prototypes with unstable pinouts, unless the mating interface is already fixed.
- High-current work better served by purpose-built power connectors instead of stuffing power into a mixed insert.
Selection Stack
01
Series
02
Shell Style
03
Shell Size
04
Insert Arrangement
05
Contact Gender
06
Keying
07
Finish
08
Backshell
09
Contacts + Tools
Build the stack from the interface outward, then lock the tooling and contact part numbers. Choosing an insert arrangement first often collides with the real shell style, contact type, backshell thread, finish, or keying.
Details That Matter
Specs that matter
- Temperature class, sealing class, and finish class.
- Contact size/type: signal, power, coax, twinax, quadrax, fiber, or thermocouple.
- Voltage, spacing, creepage, altitude, and derating for the selected insert.
- Mating cycles, vibration, fluid exposure, and blind-mate tolerance.
Backshell and shield
- Choose straight, 45-degree, or 90-degree exit from bend radius and service access.
- Terminate shields 360 degrees when EMI/RFI performance matters.
- Match plating and material to the shell to avoid corrosion and ground-path surprises.
- Specify strain relief, boot, braid, overmold, or potting before cutting wire lengths.
Sourcing and QPL
- QPL is exact-part specific. Equivalent-looking commercial parts may not qualify.
- Lock manufacturer, slash sheet, class, finish, keying, and insert before procurement.
- Use approved alternates only when the drawing or customer requirement allows them.
- Do not mix connector and backshell finishes casually on marine or outdoor systems.
MIL-DTL-38999 Shell Size And Insert Arrangement Table
Representative arrangements for connector selection and quoting. Final part numbers still depend on shell style, class, finish, keying, contact gender, and backshell choice.
| Visual | Shell Size | Insert Arrangement | Contact Count | Contact Size | Common Use |
|---|---|---|---|---|---|
 | 9 | 9-98 | 3 | 22D | Compact sensor and low-current signal circuits |
 | 11 | 11-35 | 13 | 22D | Small dense signal harness breakpoints |
 | 13 | 13-35 | 22 | 22D | Instrumentation and multi-sensor assemblies |
 | 15 | 15-35 | 37 | 22D | Dense control and I/O harnesses |
 | 17 | 17-35 | 55 | 22D | High pin-count signal interface |
 | 19 | 19-35 | 66 | 22D | Panel-to-equipment control bundles |
 | 21 | 21-35 | 79 | 22D | Large severe-environment signal layout |
 | 23 | 23-35 | 100 | 22D | Very high-density avionics wiring |
 | 25 | 25-35 | 128 | 22D | Maximum-density 38999 signal connector |
Build With This Connector
Common starting points for a MIL-DTL-38999 harness build. Send your circuit count, part numbers, or a drawing and we quote the full assembly: connectors, contacts, wire, backshells, labels, and testing.
3 ContactsConfigurator
38999 3-Circuit Sensor Lead
Series III shell 9 plug-to-receptacle lead, 3 size-22D circuits, crimped M39029 contacts, continuity tested.
Open Configurator6 ContactsConfigurator
38999 6-Circuit Signal Harness
Series III shell 9 insert 9-35 harness, 6 size-22D circuits with crimped M39029 contacts and labels.
Open ConfiguratorQPLQuote
38999 Drawing-To-Build Quote
Send the D38999 callout and we will map it to a buildable harness package.
Request A QuotePrototype-Friendly Assembly
Parts are only half the job.
MiniProto is set up for low-volume and prototype harnesses: connector sourcing, wire cutting, labeling, crimping, continuity checks, and IPC/WHMA-A-620 workmanship inspection practices. Typical lead time depends on connector availability and assembly scope.
No MOQ
Good fit for one-off prototypes, test fixtures, and pilot builds that still need a real severe-environment circular connector.
Crimp Process
Removable crimp contacts are stripped, crimped with the specified positioner and die, inserted, pull-checked, labeled, and continuity-tested.
Inspection
Workmanship checks follow IPC/WHMA-A-620 workmanship practices for strip length, crimp quality, sealing plugs, backshell, and routing.
QPL Sourcing
We quote against live availability for the exact slash sheet, class, finish, keying, and mating half instead of assuming catalog stock.
Series And Variant Choices
Series IBayonet
Fast mate/disconnect with scoop-proof interfaces for harsh moisture and vibration. A quick-disconnect option when threaded coupling is not required.
Series IILow-Profile
Lower-profile bayonet for tight panel depth or weight limits where high-vibration SWAMP exposure is not the primary driver.
Series IIITriple-Start Thread
Triple-start threaded coupling that handles vibration well. The common default for new rugged aerospace, defense, and industrial harnesses.
Series IVBreech-Lock
Breech-lock coupling for fast blind-mate disconnects in a lightweight, high-vibration connector.
Cost Drivers
Series & FinishMedium
Series III threaded parts and specific finish/temperature classes change sourcing, price, and lead time.
Contact CountHigh
Dense size-22D layouts multiply stripping, crimping, insertion, inspection, and continuity-test time.
Backshell & ToolingHigh
Backshells, band straps, boots, potting, and the specified crimp positioners and dies often dominate practical assembly cost.
Related Links
Compare Other Mil-Spec Circulars
Common Assembly Mistakes
- !Pin/socket mirrored from the wrong face. Call out wire-side versus mating-face views on drawings.
- !Wrong key or clocking. A correct insert can still be unusable with the wrong polarization.
- !No sealing plugs or filler contacts. Empty cavities and unused shield paths need the specified hardware.
- !Using generic crimp tools. Use the specified positioner, turret, die, strip length, and inspection standard.
- !Backshell chosen after layout. Exit angle and strain relief change routing, service loops, and cut lengths.
- !Ignoring finish compatibility. Mixed metals and coatings can create corrosion or bonding problems.
Part number tool
Decode or build a D38999 part number
Break a MIL-DTL-38999 Series III housing part number into plain-English segments, or assemble one from grounded options. Only slash sheets, shell sizes, and insert arrangements in our catalog are offered.
Enter a part number
ResultCheck segments
—
- (empty)
- âš Unrecognized part numberExpected form D38999/<sheet><class><shell><insert><style><keying>, e.g. D38999/26FA35AN.
Common Questions
What is MIL-DTL-38999?+
MIL-DTL-38999 is a U.S. military detail specification for miniature, high-density, circular, environment-resistant electrical connectors. A build still has to choose the exact series, shell, insert, contacts, finish, backshell, and tooling.
Which 38999 series should I start with?+
Series III is the common default for new rugged harness work because the triple-start threaded coupling handles vibration well. Series I and IV are quick-disconnect options, and Series II is for lower-profile, lower-vibration packaging.
What shell sizes and insert arrangements does 38999 use?+
Common shell sizes run 9 through 25, paired with insert arrangements such as 9-98, 13-35, or 25-35 that set contact count and contact size for the selected series.
Does every 38999 connector meet QPL requirements?+
No. QPL status is tied to the exact manufacturer, slash sheet, class, finish, and part number. If the program requires qualified product, verify the exact item in the DLA Qualified Products Database before release.
How is MIL-DTL-38999 different from MIL-DTL-26482?+
38999 is the higher-density severe-environment family with triple-start threaded and quick-disconnect series. 26482 is a miniature bayonet family used when the design does not need 38999 density.
Can MiniProto quote a harness with MIL-DTL-38999 connectors?+
Yes. Use ConfigV2 or the quote form and specify MIL-DTL-38999 along with any required part numbers, insert arrangements, keying, finishes, backshells, contacts, and QPL constraints.
How do I decode a MIL-DTL-38999 part number like D38999/26FA35PN?+
Read it left to right: the slash sheet sets the shell style (/26 is a straight plug, /20 a wall-mount receptacle), then the class letter (finish), shell size letter (A=9 through J=25), insert arrangement, contact style, and keying. The decoder tool on this page breaks any 38999 part number into those segments and links straight into a quote or ConfigV2 build.
MIL-DTL-38999 Harness Assemblies
Build the assembly, not just the connector BOM.
Configure online when the family seed lands, or send drawings and requirements now for an engineer-reviewed quote.